Heat wave conditions have abated from Rajasthan and Haryana ahead of the arrival of the weather-setter western disturbance, an India Meteorological Department (IMD) update said on Thursday.

Meanwhile, Global Forecasting System (GFS) model employed by the Climate Prediction Centre (CPC) of the US National Weather Services indicated that the trade winds in the southern Pacific have picked up steam significantly.

WIND DIRECTION

These winds turn south-west off the Horn of Africa to become south-westerly monsoon winds for India. In its update, the CPC suggested that the winds may already have changed direction along the Equator from the African coast.

Outlook until May 12 projected that the winds might decisively turn south-westerly and entrench themselves in the south Bay of Bengal while heading into the Andaman and Nicobar Islands.

Coincidentally, the US National Centres for Environmental Prediction (NCEP) has retained the outlook for the triggering of likely storm activity in the south-west Bay of Bengal during May 13 to 21.

This is forecast to hit the southeast coast of Sri Lanka en route to making an eventual landfall over the Kerala coast, as has been consistently projected over the past few days.

An experimental ocean forecast from a separate agency expected the Arabian Sea also to throw up some activity around May 25.

WESTERN DISTURBANCE

On Thursday, the western disturbance sat over Jammu and Kashmir and adjoining north Pakistan with an induced upper air cyclonic circulation over north-west Rajasthan.

The system is expected to affect western Himalayan region during the next three to four days. It may also affect the plains of northwest India.

Given this background, the heat has been confined to isolated pockets of Himachal Pradesh and is expected to abate during the next 24 hours.

The highest maximum temperature of 44.1 deg Celsius was recorded at Jhansi in Uttar Pradesh in further confirmation that the top heat was being driven away east.

The IMD has maintained the outlook for emerging volatile weather over the plains of the north-west with isolated hailstorms or thunder squalls being warned of.

Punjab, Haryana, Chandigarh, Delhi, Rajasthan and Uttar Pradesh are expected to be affected during the next two days.

Isolated thunder squalls would also occur over Jammu and Kashmir, Himachal Pradesh and Uttarkhand.

Thunder squalls are likely over Bihar, Jharkhand, West Bengal, Sikkim and the north-eastern States largely riding on the back of a prominent and semi-permanent north-south trough in the region.

On Thursday, the trough ran down from Chhattisgarh to south Tamil Nadu across Karnataka and Andhra Pradesh with embedded upper air cyclonic circulation over south Chhattisgarh.

During the past 24 hours ending Thursday morning, rainfall occurred at many places over Assam, Meghalaya and Jammu and Kashmir, the IMD update said.

A few places over Orissa and Himachal Pradesh too reported overnight rainfall. Isolated rainfall was reported from Jharkhand, north Chhattisgarh and Tamil Nadu. Satellite imagery showed convective (thundershower-causing) clouds over parts of Orissa and Punjab over land and north and south-east Bay of Bengal.

Low to medium clouds (partly clouded conditions) were seen over Andaman Sea, western Himalayan region, Rajasthan, Haryana, Bihar, West Bengal and Sikkim.

Forecast until Sunday said that fairly widespread rain or thundershowers are likely over Assam, Meghalaya and Arunachal Pradesh and scattered over Nagaland, Manipur, Mizoram and Tripura.

Fairly widespread rain or thundershowers may occur over Jammu and Kashmir during the next two days and scattered thereafter.

Scattered rain or thundershowers are likely over Himachal Pradesh and Uttarkhand during this period and isolated thereafter.

Scattered dust storm or thunderstorms accompanied with squalls are likely over Punjab, Haryana, Delhi and Chandigarh and Isolated over Rajasthan and Uttar Pradesh.

Scattered rain or thundershowers would occur over West Bengal, Sikkim, Bihar, Jharkhand and Orissa in the east and Kerala, coastal Karnataka, Lakshadweep and Andaman and Nicobar Islands in the south.

Isolated rain or thundershowers has been forecast over coastal Andhra Pradesh, south interior Karnataka and Tamil Nadu.